Hey man select 4 for sync-shoot and than you shoot the 4`th you will get slo-mo so there is time to kill another 2 soldier, this is how i managed to kill 4 to 8 enemies with sync shoot just try it. anyway wait till the 4th one close to someone else than boom 3-4 sec slowmotion killthemall!!!!!!!!!!!!
So guys get the snipers off the roof , before you kill anyone else , make shure the dead collapse behind something , dont kill anyone first in the open!!!!!! first snipers than soldiers behind something than enemies in the open, good luck